The function of transfer assist blades is generally for pressing a copy substrate into intimate contact with the toner particles on a selectively charged imaging surface, for example, the photoreceptor, during image transfer from the charged imaging surface onto the copy substrate. In particular, non-flat or uneven image support substrates, such as copy sheets that have been mishandled, paper that has been left exposed to the environment, or substrates that have previously passed through a fixing operation (for example, heat and/or pressure fusing) often tend to yield imperfect contact with the photoconductive surface. Some printing applications require imaging onto high quality papers having surface textures which prevent intimate contact of the paper with the developed toner images. In duplex printing systems, even initially flat paper can become cockled or wrinkled as a result of paper transport and/or the first side fusing step. Also, color images can contain areas in which intimate contact of toner with paper during the transfer step is prevented due to adjacent areas of high toner pile heights. The lack of uniform intimate contact between the belt and the copy sheet in these situations can result in spaces or air gaps between the developed toner powder image on the selectively charged imaging surface and the copy substrate. When spaces or gaps exist between the developed image and the copy substrate, various problems may result. For example, there is a tendency for toner not to transfer across gaps, causing variable transfer efficiency and, under extreme circumstances, creating areas of low toner transfer or even no transfer, resulting in a phenomenon known as image transfer deletion.
In order to minimize transfer deletions, transfer assist blades (TABs) have been utilized to press the back of the copy substrate against the imaged area of the charged imaging surface. Variations and improvements upon transfer assist blades are well known in the art. See, for example, U.S. Pat. No. 4,947,214 issued to Baxendell, et al.; U.S. Pat. No. 5,227,852 issued to R. Smith et al.; U.S. Pat. No. 5,300,393 issued to Vetromile; U.S. Pat. No. 5,300,994 issued to Gross et al.; U.S. Pat. No. 5,539,508 issued to Piotrowski et al.; U.S. Pat. No. 5,613,179, issued to Carter et al.; and U.S. Pat. No. 5,568,238, issued to Osbourne et al. In each of these disclosures, the transfer assist blade is moved from a nonoperative position spaced from the copy substrate, to an operative position, in contact with the copy substrate for pressing the copy sheet into contact with the developed image on the photoconductive or other charged imaging surface in order to substantially eliminate any spaces therebetween during the transfer process. The entire disclosures of the above-referenced patents are hereby incorporated by reference for their relevant teachings.
As a specific example from the above list of patents, U.S. Pat. No. 5,247,335, issued to: R. Smith et al. discloses a transfer assist blade for ironing a sheet against a photoreceptor belt during transfer, thereby smoothing out deformities that cause deletions. The transfer assist blade includes a flexible tip to absorb the impact of the blade as it contacts the paper arid a spring load to limit and control the force applied to the sheet.
As taught in the prior art, no portion of the transfer assist blade should contact the imaging surface since such contact will result, in ;Most instances, in the pick up of residual dirt and toner from the charged imaging surface onto the portion of the transfer assist blade that contacts the imaging surface. Also, contact by the TAB onto the charged imaging surface risks abrading such surface, therefore adversely affecting subsequent image quality and shortening the expected life of the expensive photoreceptor or other charged imaging surface. In order to ensure that a transfer assist blade contacts the COPY sheet only within the copy substrate perimeter, either the transfer assist blade must be shortened to correspond to the narrowest copy sheet width expected to be processed in the printer or there must be added an apparatus for detecting the width of each copy sheet and varying the effective length of the transfer assist blade to correspond to the width of such sheet. Apparatus such as those disclosed in U.S. Pat. No. 5,300,994 and U.S. Pat. No. 5,539,508 are capable of varying the effective length of the transfer assist blade when operating in conjunction with appropriate sensors and algorithms.
The described ability to vary the length of the TAB enables the TAB to be adjustable in the direction perpendicular to the paper path. For the same reasons that the length of the TAB may be adjusted, it is also important that the TAB be raised and lowered so as not to contact the photoreceptor or other charged imaging surface. As a counterpoint, it is also important that the TAB contact the back of the copy substrate as close as possible to the leading and trailing edges of the copy substrate in order to ensure contact in all imaging areas. A high degree of accuracy is therefore required in timing engagement and disengagement of the TAB with the copy substrate. Such engagements and disengagements of the TAB are generally designed as timed sequences in relation to paper path speed and the sensed width in the paper path of the copy substrate. As an example, U.S. Pat. No. 6,556,805, issued to Kuo et al., teaches a method of activating TAB segments by rotating one of more cam shafts, thereby pressing the TAB into contact with the copy substrate when the appropriate cam lobe has been rotated sufficiently to press the TAB toward the copy substrate. Another system for activating TAB motions is taught in U.S. Pat. No. 6,188,863, issued to Gross et al. Any number of other systems have been utilized and many more are possible.
In the cam system taught by U.S. Pat. No. 6,556,805 and in other TAB cam systems, there is a timing delay between commencement of rotation by the cam shaft and contact between the TAB and the copy substrate. Other activation systems also have such delays between activation of the system and contact between TAB and copy substrate. Similarly, there is a timing delay between sensing of the leading or trailing edge of a copy substrate and actuation or deactivation of the cam shaft rotation or other mechanism that urges the TAB toward the copy substrate. Such timing sequences are typically handled during machine design and initial system calibration. Conventionally, the calibration is performed manually by such means as attaching an ink pad to the blade, measuring the length of the mark that the pad makes on the back of a copy sheet, and calculating the required adjustment time to achieve the desired length of such mark.
As printing system speeds increase, the speed of the copy substrate along the paper path increases, and TAB activation and deactivation must be timed more perfectly to ensure proper placing of the TAB as close as possible to the leading and trailing edges. Moreover, initial calibrations of the timing sequence may be obsoleted as components affecting the sequence are replaced over time with replacement components that vary slightly in response time, size, shape, etc. In particular, a replacement TAB can vary slightly in length, thickness, position within its mounting, and each of these factors may affect the timing of TAB contact with a copy substrate. Additionally, normal wear and tear and “settling in” of cams, motors, gears, photoreceptor belts, and other components can affect the precise timing sequence of TAB actuation apparatus. Additional calibrations are possible but typically require the time, expense, and labor of service and maintenance calls. It would be advantageous for electrostatographic imaging systems utilizing TAB-type devices to have an automated timing adjustment system wherein the timing of TAB activation and deactivation is automatically adjusted in response to any of the changes that may affect the TAB timing sequence.
In accordance with the claimed embodiments, there is provided an apparatus for adjusting the timing of contact between a transfer assist blade and a charged imaging surface in order that the timing be automatically adjusted within specifications, said apparatus comprising: an imaging apparatus for developing a partially toned pattern having about 20 to about 80 percent coverage in a region of a charged imaging surface; a transfer assist blade assembly, including a transfer assist blade, for moving a transfer assist blade between a position engaged with a surface and a position disengaged from such surface; a drive device, connected to the transfer assist assembly, for imparting engagement and disengagement motion to the transfer assist blade, said drive device having an activation time for engaging the transfer assist blade with the surface and a deactivation time for disengaging the transfer assist blade from the surface; a toner area coverage measuring device for measuring the percentage of the partially toned region that is covered by toner; and a controller, in communication with the drive device and area coverage measuring device, for adjusting the timing of activation of the drive device, wherein, in response to receiving signals from the toner area coverage measuring device indicating that the time of activation resulted in engagement of the transfer assist blade outside of the specifications, the controller adjusts the timing of activation accordingly.
Pursuant to another aspect of the claimed embodiments, there is provided an electrostatographic imaging system having specifications for engaging a transfer assist blade with a charged imaging surface, comprising: a charged imaging surface; an imaging apparatus for developing a partially toned pattern having about 20 to about 80 percent coverage in a region of a charged imaging surface; a transfer assist blade assembly, including a transfer assist blade, for moving a transfer assist blade between a position engaged with a surface and a position disengaged from such surface; a drive device, connected to the transfer assist assembly, for imparting engagement and disengagement motion to the transfer assist blade, said drive device having an activation time for engaging the transfer assist blade with the surface and a deactivation time for disengaging the transfer assist blade from the surface; a toner area coverage measuring device for measuring the percentage of the partially toned region that is covered by toner; and a controller, in communication with the drive device and area coverage measuring device, for adjusting the timing of activation of the drive device, wherein, in response to receiving signals from the toner area coverage measuring device indicating that the time of activation resulted in engagement of the transfer assist blade outside of the specifications, the controller adjusts the timing of activation accordingly.
In accordance with yet another aspect of the claimed embodiments, there is provided a method for automatically adjusting the timing of engagement of a transfer assist blade with a charged imaging surface, comprising: commencing a sequence for adjustment of the engagement timing; developing a partially toned pattern having about 20 to about 80 percent coverage in a region of the charged imaging surface; activating a drive device that moves a transfer assist blade from a disengaged position to an engaged position at a time estimated to engage the transfer assist blade within a specified portion of the partially toned region; reading, by a controller, a signal from a toner area coverage sensor indicating the portion of the partially toned region that is smeared by the transfer assist blade; determining, with a controller, from the signal from the toner area coverage sensor, whether the transfer assist blade engaged the charged imaging surface within specifications; adjusting, in response to determining that the time of engagement was not within specifications, the time of activation of the drive device in order to meet specifications.